Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$53.32	12.599%	$60.0378	$60.04	$60.05	$60.00
Purchase #2	$52.47	9.679%	$57.5486	$57.55	$57.55	$57.50
Purchase #3	$37.86	13.693%	$43.0442	$43.04	$43.05	$43.00
Purchase #4	$132.82	11.165%	$147.6494	$147.65	$147.65	$147.60
Purchase #5	$130.42	5.372%	$137.4262	$137.43	$137.45	$137.40
Purchase #6	$16.72	3.574%	$17.3176	$17.32	$17.30	$17.30
Purchase #7	$88.98	12.228%	$99.8605	$99.86	$99.85	$99.90
7 purchase totals =	$512.59		$562.8843	$562.89	$562.90	$562.70